The automotive industry, in order to reduce the number of wires which must be run to electrical and electronic modules located in different parts of a vehicle, has evolved to a distributed type of multiplexed control. This distributed control arrangement utilizes computers located at certain of the modules which are connected together via a twisted pair, or coaxial or fiber optic cables, in a computer communications network. In order to communicate effectively between the various in-vehicle modules, Robert Bosch GmbH and Intel Corporation introduced a set of communication rules or protocol at the Society of Automotive Engineers trade show in February, 1986, which is currently implemented in the Intel 82526 Serial Communications Controller. This protocol, which is called CAN for "controller area network", supports a network of multi-master nodes, performing non-destructive bit-wise arbitration of messages with functional addressing.
It would be desirable to be able to use the serial communications controller chips, such as the Intel 82526, developed for in-vehicle networking, in refrigeration related applications, such as in transport refrigeration systems or units.
The fixed message frame format of the CAN protocol, however, while suitable for automotive use, is too limiting for the communications involved between refrigeration related control modules. For example, large amounts of information are required to be collected and transmitted between different refrigeration control modules, which information is operated upon by diagnostic programs, with system status, along with specific detected alarm conditions being displayed locally and/or remotely. Raw data, system status and alarm conditions must be readily available for remote monitoring functions. Examples of remote monitoring functions include remote monitoring arrangements which utilize electric power lines, including ship-board wiring in container refrigeration applications, satellite communications in over-the-road truck and trailer refrigeration applications, and the like. The information must also be readily available for down loading via plug-in data loggers, and refrigeration controls must be able to be initialized to a predetermined application by a plug-in data pack, and quickly and easily re-initialized to accommodate a different conditioned load having different refrigeration requirements, including temperature, humidity, and special protective atmospheres, such as by downloading specific program constants and/or application specific programs to a central computer node and/or flash programmable read-only memories (PROM) in the distributed network.